McALLEN, Texas — Corruption along the U.S.-Mexican border takes many forms. It can start as simply as a smuggler's $50 gift to the child of a reluctant federal agent, quickly escalating to out-and-out bribes. "Everyone does it," the agent, now in prison, recalls telling himself. Other times, county sheriffs greedily grab thousands from drug dealers. In a few instances, traffickers even place members in the applicant pool for sensitive border protection jobs.

An Associated Press investigation has found U.S. law officers who work the border are being charged with criminal corruption in numbers not seen before, as drug and immigrant smugglers use money and sometimes sex to buy protection, and internal investigators crack down.

Based on Freedom of Information Act requests, interviews with sentenced agents and a review of court records, the AP tallied corruption-related convictions against more than 80 enforcement officials at all levels — federal, state and local — since 2007, shortly after Mexican President Felipe Calderon declared war on the cartels that peddle up to $39 billion worth of drugs in the United States each year.

U.S. officials have long pointed to Mexico's rampantly corrupt cops and broken judicial system, but Calderon told the AP this isn't just a Mexican problem.

"To get drugs into the United States, the one you need to corrupt is the American authority, the American customs, the American police — not the Mexican. And that's a subject, by the way, which hasn't been addressed with sincerity," the Mexican president said. "I'm waging my battle against corruption among Mexican authorities and we're risking everything to clean our house, but I think there also needs to be a good cleaning on the other side of the border."

‘Weakness in the armor’In fact, U.S. prosecutors have been taking notice. Drug traffickers look "for weaknesses in the armor," said former prosecutor Yolanda de Leon in Cameron County, Texas.

One such weakness was her own county's Sheriff Conrado Cantu. With his thick mustache, ample belly and Western hat, Cantu was a backslapping natural in the political machine of Cameron County, population 335,000. The county includes Brownsville, Texas, directly across the Rio Grande from Matamoros, Mexico.

In no time, Cantu rose from constable to sheriff, a job he later acknowledged he was unqualified to hold. In 2005, he pleaded guilty to federal charges of running a criminal enterprise involved in extortion, drug trafficking and bribery. He's now serving a 24-year sentence for extorting money from drug traffickers and illegal gambling operations.

"If the opportunity came along, he would take it," said de Leon.

Not all corruption charges that turned up in AP's checks were related to drug trafficking. The researched cases involve agents helping smuggle immigrants, drugs or other contraband, taking wads of money or sexual favors in exchange — or simply allowing entry to someone whose paperwork isn't up to snuff, all part of the daily border traffic that has politicians demanding that the U.S.-Mexico border be secured.

Court records show corrupt officials along the 2,100-mile U.S.-Mexico border have included local police and elected sheriffs, and officers with such U.S. Department of Homeland Security agencies as Immigration and Customs Enforcement, and Customs and Border Protection, which includes Border Patrol. Some have even been National Guardsmen temporarily called in to help while the Border Patrol expanded its ranks.

‘High-threat environment’As Calderon sent thousands of soldiers to northern Mexico to stop the gruesome cartel violence and clean out corrupt police departments, CBP, the largest U.S. law enforcement agency, boosted its border forces by 44 percent or 6,907 additional officers and agents on the southwest border.

At the same time, CBP saw the number of its officers charged with corruption-related crimes nearly triple, from eight cases in fiscal 2007 to 21 the following year — and began to crack down.

"Day in, day out, someone in our agency is approached and says no, but we operate in this high-threat environment," said James Tomsheck, assistant commissioner for internal affairs at CBP. "The reality of it is we are deeply concerned."

In the past 10 months, 20 agents from CBP alone have been charged with a corruption-related crime. At that pace, the organization will set a new record for in-house corruption; 90 employees have been charged with corrupt acts since October 2004. Agency officials expect those cases to continue to climb: There are 63 open criminal investigations — including corruption cases — against CBP employees.

At least as unsettling were the prospective agents who never got to commit their crimes: Four applicants for jobs in federal border law enforcement were not hired when polygraph tests and background checks confirmed they were infiltrators from drug trafficking operations, authorities said.

Such in-depth checks are conducted on only about 10 percent of applicants for border agent jobs, though such scrutiny will eventually be made standard for all applicants, according to Tomsheck. Meantime, officials are left to wonder: Are other gangsters working undercover for agencies charged with protecting the U.S. border?

More checks in-houseCBP had more than 2,000 in-house discipline cases during the past three years, according to records obtained by the AP under the Freedom of Information Act. Most were minor, but about 100 reflected more serious, corruption-related incidents, many of which were later prosecuted.

The jump in corruption cases comes as CBP has increased its team of internal investigators from five three years ago to 220 today.

CBP's own investigation of corruption cases showed little correlation between minor disciplinary problems and the more serious instances of bribery and malfeasance.

"Virtually none of the employees arrested for corruption are employees that have serious misconduct issues," Tomsheck said. "Actively corrupt employees do everything they can to stay below the radar screen."

It can be heartbreaking to see agents switch sides for small amounts of money, said U.S. Attorney Tim Johnson, whose turf covers a long stretch of border from the Gulf of Mexico to Laredo, Texas. But, Johnson and other federal prosecutors say, "these cases will always have a priority" and must be prosecuted "to the fullest extent," to emphasize that corruption will not be tolerated.

"You can't allow people who work within the law enforcement community to compromise our mission. We would just lose control of everything down there," he said.

It's a lesson Mexico learned the hard way, ignoring for years corrupt police until Calderon began to replace them with military personnel.

In Texas, which has more than half the U.S. border with Mexico, the commission that oversees state and local law enforcement officers reported that criminal misconduct cases were opened against 515 officers in fiscal 2007 and 550 officers in fiscal 2008. Some form of disciplinary action was lodged against 324 and 331 peace officer licenses, respectively, in those years.

"The cartels increasingly recruit law enforcement officers on both sides of the border," Steve McCraw, then Texas's homeland security chief, told state lawmakers earlier this year. "It's not just a Mexico problem because of the amount of money involved. And as we've increased presence between the ports (of entry), there's an increased desire to recruit law enforcement personnel to move across the bridge or use them between the ports."

Low-level agent is ‘incredible bargain’In-house CBP data shows corrupt agents fall into two categories — recent hires who are charged very quickly, indicating they took the jobs intending to break the law, and veteran agents who have worked for the agency for a decade or more before succumbing to the offers.

"From the Mexican cartels' point of view, it is cheaper to pay an official several thousand dollars to allow a load of narcotics to pass by than it is to risk having the shipment seized," Scott Stewart and Fred Burton, vice presidents of global intelligence firm Stratfor, wrote in a recent report. "Such bribes are simply part of the cost of doing business — and in the big picture, even a low-level agent can be an incredible bargain."

One such officer, a CBP agent convicted of taking money to smuggle illegal immigrants, was over his head with credit card debt, behind on child-support payments, about to lose his truck. His 10-year-old, whom he had taken to the mall for the day, wanted a football he couldn't afford.

That's when a friendly, familiar Mexican man pulled a $50 bill from a thick wallet and handed it to the agent's son, who snatched the money and dashed off to the Dallas Cowboys Pro Shop.

The father related the story in the visiting room of a federal prison in California where he is serving a four-year term.

"I was like, 'Wait son, hang on!' but he was gone, so happy with that money," said the former agent, whom prison officials allowed the AP to interview on condition of anonymity because convicted law enforcement officers are considered potential targets.

That was how it began, the ex-agent continued. A few weeks later, the Mexican man suggested that the officer let a man through his pedestrian checkpoint early one morning without asking questions. He'd get $5,000 for his trouble.

"I thought, 'Naaah, I can't do that.' Then I thought, 'Hell, my life's a mess. Everyone does it. If I'm caught I'll just say the guy got past me. I'll do it once. I could use the money,'" he recalled.

The cash came in handy. He bought clothes for his kids, jerseys for a youth team he coached; he made his truck payment, caught up on credit card bills.

The next time was easier, if less lucrative: $1,500 a person.

Nervously smoothing his prison-green scrubs, he said, "I really planned to stop." But then another offer came, even while colleagues warned him the FBI was snooping around. And then a woman he had illegally passed through named him when she was caught by an honest agent.

He was convicted for passing one person through. He paid $5,000 in fines in addition to the prison term.

"You want to know how many times I did this?" he asked. "Sixty-six. I kept a tally."

Lines blur in border communitiesThe men and women who were caught described their jobs as prestigious and well paid for the small border towns where they grew up. An entry-level CBP officer earns $37,000 a year in Laredo, and within a year is likely paid $41,000, well above the local average annual income of $25,000.

In border communities, the demarcation between countries is insignificant. People live on one side, work on the other; have a favorite barber on one side, but buy groceries on the other. The traffic is heavy, and constant.

Some of the border authorities were born in Mexico or are related to Mexican nationals. So do you let a colleague's Mexican aunt cross the border without a visa for a family birthday party? Or wave through a loaded truck that belongs to your bosses' brother-in-law without looking inside? Some agents said yes.

And so did some state and local officers. The deputy commander of a narcotics task force was caught in a sting operation protecting what he believed were loads of drugs moving through Zapata County; others have shaken down drug traffickers moving product through their turf.

In October, FBI agents arrested Starr County Sheriff Reymundo Guerra at his office as part of a sweep dubbed "Operation Carlito's Weigh." Guerra, the chief law enforcement officer for the border county of 62,000 people, had spent a decade as sheriff.

There was little public pressure for his ouster after his arrest and since he was running unopposed, Guerra was re-elected weeks later. County Judge Eloy Vera said the day of his arrest that Guerra, a mustachioed bear of man, was a "very good sheriff." He resigned only as a condition of his release pending trial.

In May, Guerra pleaded guilty to a drug trafficking charge for accepting thousands of dollars in exchange for passing information to a former Mexican law enforcement contact who he knew was working for Mexico's Gulf Cartel. Guerra once even gave false documents to one of his own deputies to close a drug trafficking investigation, prosecutors said.

Guerra could face up to life in prison when he is sentenced later this month.